Stellar Core Fusion: pp-Chain vs CNO Cycle

Every main-sequence star burns hydrogen through two different nuclear pathways that scale with core temperature at wildly different rates: the proton-proton chain grows roughly as T⁴, while the carbon-nitrogen-oxygen cycle grows as roughly T¹⁸. This simulator renders a star's core in 3D as a live field of fusion "sparks," colored by which chain produced them, with their populations driven directly by the two rate formulas — calibrated so the Sun's own core (15.7 million K) reproduces its real 98.5%/1.5% split. Drag the temperature, hydrogen-fraction and metallicity sliders (or jump to Sun / Sirius A / metal-poor presets) and watch the core swing from pp-blue to CNO-orange as it crosses the live-computed crossover temperature.